HTML: Sub-pixel border

Question

Is it possible to have a border that is thinner than 1px and works in IE6+ and is not an image and renders properly visually?

Thank you.

Answer 1

As of mid 2020, current versions of Safari and Firefox both support border-width: .5px.

On the other hand, Chrome will treat it as 1px.

You can detect whether the browser supports it with something like:

var el = document.createElement('div');
el.style.position = 'fixed';
el.style.borderTop = '.5px solid';
document.body.appendChild(el);
var hasSubpixelBorder = el.getBoundingRect().height < 1;
document.body.removeChild(el);

Make sure this is called after document.body is created if you are doing it at startup.

If this is not supported (e.g. Chrome) you can add a class to document.body or some parent element to cause descendants to take on a different border style:

@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 2dppx) {
    .noSubpixelBorder .border-top {
        border-top-width: 0;
        background-image: linear-gradient(180deg, var(--mycolor) 0, var(--mycolor) .5px, transparent 0);
    }
}
@media (-webkit-min-device-pixel-ratio: 3) and (-webkit-max-device-pixel-ratio: 3.5), (min-resolution: 3dppx) and (max-resolution: 3.5dppx) {
    .noSubpixelBorder .border-top {
        background-image: linear-gradient(180deg, var(--mycolor) 0, var(--mycolor) .333333px, transparent 0);
    }
}

You can use multiple linear gradients to achieve borders on multiple sides. This takes over background-image so if you are using it for something else you will need to find another way (there are a couple others).

This is not particularly clean, but it seems to consistently work.

If you wanted to be super crafty, you could support oddball pixel ratios by computing the stylesheet on the fly.